Posted
by
ScuttleMonkeyon Sunday August 06, 2006 @04:21PM
from the seismic-remodeling dept.

Science Daily is reporting that scientists were able to use satellite data to watch changes in the Earth's surface caused by a massive earthquake. These changes had two major measurable effects on the region. The massive uplift in the seafloor changed GPS measurements, and the density of the rock beneath the seafloor changed which produced a detectable change in gravity.

I have a lot to keep track of, what with my checkbook, blogs, email, vehicle oil changes and tire rotation, bills, and keeping various client networks running.

So I'd appreciate it if someone could keep track of this whole gravity situation, and just give me a summary. Let me know if we're all about to go floating off into LEO, but otherwise, keep the announcements to a minimum.

Detecting "major" quakes - those measuring a magnitude of 7 to 8.9 - which occur frequently is being investigated. NASA's planned extension of the current mission, dubbed GRACE 2, and its enhanced instrumentation should aid in that effort.

However, Han is hopeful that NASA's planned expansion of the current mission, dubbed GRACE 2, and its enhanced instrumentation, might allow the detection of "major" quakes - those measuring a magnitude 7 to 8.9 - which occur frequently.

Detecting "major" quakes - those measuring a magnitude of 7 to 8.9 - which occur frequently is being investigated. NASA's planned extension of the current mission, dubbed GRACE 2, and its enhanced instrumentation should aid in that effort.

However, Han is hopeful that NASA's planned expansion of the current mission, dubbed GRACE 2, and its enhanced instrumentation, might allow the detection of "major" quakes - those measuring a magnitude 7 t

If we don't take this threat seriously, we will all be smashed flat, like pancakes, and grilled by global warming.

Unconfirmed reports indicate that giant bird-like aliens will arrive shortly, and revel in the pancake carnage, gorging on the waste like so many crows on road kill. The same sources said they do not wish to imply that the aliens are in

Really bland article I mean I can change the gravitation fields on my desk my moving my glass of water around and I do believe that is measurable. (Maybe not by a satellite.) So anyone out there have an idea of the magnitude of the change. Will athletes gain a boost there by training in a higher gravity environment? What are the effects of the lower gravity environment or is it so insignificant that who cares.

Or more interesting dose anyone have a map of the earth and differences in gravity in different areas? (I smell a new google map)

Will athletes gain a boost there by training in a higher gravity environment?

Of course, sport is more important than science! Why don't you go measure the gravity effects of your glass of water? Oh, that's right, you don't know how to do that. This may not be a groundbreaking development, but it may be a newsworthy accomplishment.

Will athletes gain a boost there by training in a higher gravity environment?

I've just done extensive research over whether Superman is more powerful than Goku, and I must say very well respected researchers in both fields are at a stalemate. Since a lot of Goku's adult training was in higher gravity levels, I can answer your question emphatically yes.

The effect is well in line with the natural distribution of the local gravity constant.Meaning it should be in the 0.01 m/s^2 range.

For the simple reason that if it were anymore, the earth would deform to counter that imbalance (molten core, you know).That, btw, also limits the height of mountains to about 10-12Km on earth (compare to mars, where to lower gravity constant allowed much larger volcanos)

So anyone out there have an idea of the magnitude of the change. Will athletes gain a boost there by training in a higher gravity environment? What are the effects of the lower gravity environment or is it so insignificant that who cares.

The full paper as well as a very nice layman's introduction in the Perspectives section is in this month's issue of Science. (Sorry - subscription only. But you may be able to find the text on a preprint server. I'm no geologist, but I haven't been able to find it in any of the obvious places.)

Basically, they map out a change of 15 microgals (1 gal = 1 cm/s^2) or around 1.5e-8 of the average gravitational field on the earth.

By comparison, the variation in g with latitude (at constant elevation) is around 0.5 percent, or 300'000 times as much. Variation associated with local geology is around 100 times smaller, but still swamps this earthquake signal.

What's cool about this measurement isn't that they're measuring something big enough to have any effect on humans, but rather that they're able to measure such a tiny effect at all.

There are all sorts of processes going on in the earth and in the oceans that involve movements of comparable amounts of mass: changes in glacier and polar icecaps, ocean-atmosphere gas exchange, deep sea current and temperature changes, movement and depletion of underground water, fast moving magma associated with volcanos, slow tectonic changes, etc. And now it seems like it's also helpful in trying to construct detailed models of an earthquake.

Incidentally, if you were an athlete trying to cash in on lower gravity, you'd be better off training in the Chilean highlands and competing in Puerto Rico - but it still wouldn't help you much, especially compared to biological effects and day to day variation in performance. (http://www.csr.utexas.edu/grace/publications/fact _sheet/3.html)

you could do the same thing by strapping on weights to yourself, set up so that the weight distrabution is the same as "normal". or alternatively, they could just do normal resistance/weight training with more weights... maybe run with some sandbags strapped to the legs. its really a lot simplier that way.

Load of crap!
The Earth's gravity can only change with added or reduced mass. This article hints that it is the amount of gravity that has changed which isn't possible through this earthquake. What is possible is that the vector of gravity; (typically down twards the center of the earth) has been changed since dense matter has moved drastically.

On a side note, the earth tends to pick up 200 lbs every year due to meteorites. If there's any change in the ammount of gravity, that is what's doing it!

The same amount of gravity is there, as before the earthquake. That has not and cannot change. What has changed is which direction (or as I called it, "vector") that the gravity is pulling.
As the vector changes, your one dimentional equipment for measuring gravity is sure to have a change in values. Go back to Highschool Trig.

Let's say that you are on the surface of a planet that is constructed from two hemispheres of equal size. The northern hemisphere is composed of aluminum and the southern hemisphere is composed of iron. You take gravity measurements at the north and south poles. What are your results?

Ahhhhh, but the increase in gravity due to mass is linear. Double the mass, double the force.

But the force of gravity also follows the inverse square law, get twice as far away and you quarter the force of gravity.

So if your added mass necessarily pushes you farther away from the center the force will fall off due to distance faster than it increases due to mass, lowering the net force, unless your cement block is very massive. Say about 1000 Kg.

Sorry to burst your bubble, but I think you mean a local gravity decrease. Why use one cement block when you could use a million? Take it to the limit! When you step on the cement block(s), you're moved farther away from the center of the earth. The effects of gravity decrease with the square of the distances involved. And I think you can agree that the mass of a million cement blocks will not change the center of mass of the Earth enough to compensate.

When you step on the cement block(s), you're moved farther away from the center of the earth....and closer to the center of the cement block. Distance is going to be a bigger factor in terms of the cement block's gravity vs. the Earth's; realtive to your mass & size, Earth is so many billions of orders of magnitude bigger than you; whereas ten or fifteen cement blocks might equal your mass and exceed your density (and Earth's, at the surface anyway).A terrestrial mass only a couple of kilometers in di

So what happens when I fart? . ..I've stood on a bathroom scale trying to measure this but my instruments are either too insensitive or are too greatly affected by the tremendous resultant atmospheric change. Any ideas?

Use a satellite.

Contemplate other phenomenon that might affect the outcome of the experiment (hint: think of a balloon) and propose a means of compensating for their effect.

If the satellite turns out to be insufficiently precise ponder the limits of measurment and the concept of significance

Put a cement block on the floor in front of you. Now stand on it.
Ta da! Instant local gravity increase, because there is now more mass underneath you.

Really?

What I mean is this: does the extra attractive force between you and the cement block more than compensate for the extra distance you've put between yourself and the earth's center of mass (which would tend to decrease the gravitational force you feel from earth)?

does the extra attractive force between you and the cement block more than compensate for the extra distance you've put between yourself and the earth's center of mass

Gravity falls off by the inverse of the square of the distance. If your cement block is equal in mass to the average of the column of Earth underneath you the mass is only going up linearly with distance and the total force will go down. If it's equal to the square of the average mass you'

What we really want to know is can this data be fitted to measurements immediately before the quake. Since earthquakes are essentially relaxation oscillations in plate movement very careful extrapolation with some fancy signal processing techniques (linear prediction maybe) might be able to spot some features in the gravity field out in space.I think there's no magic bullet for quake prediction, but the solution is a very holistic thing by aggregating lots and lots of different measurements. For example the

If half of the Earth moves relative to the other half, which set of property owners has a problem?

If it moves "a little", the people with a problem with be the ones that are poorer - as usual. By definiton the more well-to-do have the means to fix stuff (or higher a better lawyer to get the "new" property lines drawn in their favor:-)

On the other hand, if it moves "a bit", (like "end of the world as we know it") then maybe you would have been better off as a hunter gatherer, already in tune with the pr

If GPS is tied to some NAVY building in Maryland and the building moves, do we then declare that the building DID NOT MOVE because it is by definition in a particular place? Everybody else moved?

Uhhhhh... somebody correct me if I'm wrong, but so far as I was aware, the only thing GPS is "tied to" is a ring of satellites in geosynchronous orbit above the Earth, where they are mostly indifferent to earthquakes. Just because this article (rather vaguely) says that "GPS measurements" changed doesn't mean th

When you get a position fix from the GPS system, you are combining the information from several satellites, each of which is transmitting a signal of the form, "My name is GPS _X_, I sent this message at time _Y_ from the approximate location _Z_" A GPS receiver triangulates a position by calculating the distance to several satellites, using Center-Of-Earth coordinates.

It's true that your position is calculated relative to the satellites, but in order for the satellite to know where it was when it sent the message, there has to be pretty accurate data about its precise orbit, which depends intimately on the shape and mass distribution of the earth ("Geosynchronous" is only approximate), so that the final location in Latitude.-Longitude.-Altitude can be given relative to the center of the earth. A big quake could certainly shift things around enough to alter the orbit, which is probably what these researchers were talking about.

On the other hand, for the purposes of surveying on earth, its certainly conceivable that one could define property lines in relation to the locations of particular GPS antennae, fixed into bedrock or something, and that if those moved, things would be all kerflooey. But that's not new to GPS surveying, since its always been done relative to the location of particular fixed monuments.:)

Perhaps your GPS unit thus gives you a position relative to the average of those sites. That would be two spots in the Pacific Ocean, one in the Indian Ocean, one in the South Atlantic Ocean, and one in the Rocky Mountains. If things disagree, I'll bet Colorodo Springs wins the argument.

GPS coordinates are relative to the center of gravity of the Earth (i.e. average position of all the mass on Earth) and the rotation axis of the Earth. Longitude is tracked by measuring the average rate of rotation from pulsar signals received in several radiotelescopes around the earth.It's all based on averages. The motion of the crust in the biggest earthquakes is still insignificant compared to the total mass of the entire volume of the Earth so it doesn't really affect the GPS frame of reference. The e

This reminds me a little of a physics practical I did this year. It was supposed to be the first practical where we would get a decent accuracy, measuring g using a pendulum to about 6 significant figures.

We were also told at the end of the practical about far more accuarte ways of measuring g, and that a university in Germany several decades ago had used this regularly as experimental training for graduate students. However, when the experiment was performed at different times of the year, a small but definte increase in g was noticed during the winter. More accurate measurements showed a sudden spike near the start of winter, followed by a slow decrease until the summer.

Professors were baffled, until someone remembered that the lab in which the experiments were carried out was above a coal cellar used to store a huge quantity of coal for burning during the winter.

Very interesting. IAAPM (I am a physics major) and wonder how you can get 6 significant figures from a pendulum. Can you describe the experiment? Was it a simple pendulum, a weight at the end of a wire? Or can you point to a web page with some details? Thanks.

Sorry, my mistake, the experiment was done at the start of this year and I didn't remember the details. I've now got my lab notes in front of me , and it was only really accurate to 4 significant figures, although I think the error was small enough that we recorded 5 figures. The experiment is done in the first year of the natural sciences tripos in Cambridge, I'm not sure if you can find details on line though. No, the pendulum was not simple, its moment of inertia had to be measured using it as a torsion